The risk to women of contracting the AIDS virus increases with repeated sexual exposure to an infected man and through anal intercourse, researchers at the University of California at Berkeley reported yesterday.

The researchers studied 97 women, from ages 19 to 65, who had had sexual relations with 93 AIDS-infected men in the year before infection among the men was detected.

The chances of contracting acquired immune deficiency syndrome, or AIDS, through heterosexual sex are low, but "it's still Russian roulette," said Nancy Padian, who directed the study published in the Journal of the American Medical Association. "The fact that the infectivity of this virus to heterosexuals is low has to be tempered by {the fact that} this is a lethal disease for which there is no cure."

Padian and her colleagues sought to determine the risk of infection to women sexually exposed to men carrying the AIDS virus. Their study found that only repeated sexual contacts by a woman with the infected man and the practice of anal intercourse increased her chances of acquiring infection.

Of 65 women who had had more than 100 sexual encounters with their infected mate, 20 (or 31 percent) themselves became infected, the researchers found.

"Indeed, while this is evidence that male-to-female transmission occurs, what remains striking is how many people do not become infected," Padian said. "This is a hard disease to transmit."

Having multiple sex partners, a known risk for homosexual men, did not raise the chance of women becoming infected in this study, probably because the pool of infected heterosexuals is low, she said.

The risk of males contracting AIDS from females was not addressed in the study, but it is generally believed to be equal or lower than for women, she said.

Padian said these facts should not detract from the public health message that sexually active people must be selective about partners and use condoms when the partner's infection status is unknown.

As of Monday, 40,051 cases of AIDS and 23,165 deaths had been reported to the federal Centers for Disease Control. Of those, 1,532 cases, or 4 percent, were classified as heterosexually transmitted.